This invention relates to wireless digital communication systems, and in particular to microcellar packet communication systems, employing frequency hopping spread spectrum techniques.
As personal wireless communication systems such as in cellular telephony proliferate, the spectrum available to the wireless user for accessing cell sites for interactive communication becomes premium. There is great pressure to shrink the cell size of cellular telephone systems, for example, in order to promote frequency reuse and ultimately increase user density and capacity, as well as to reduce the required transmitter power for battery-operated portables. This is part of the trend toward so-called microcellar systems.
An example of such a microcellar system is U.S. Pat. No. 5,515,369 entitled xe2x80x9cMethod For Frequency Sharing And Frequency Punchout In Frequency Hopping Communications Networkxe2x80x9d inventor George Flammer, III, et. al. issued May 7, 1996, (herein xe2x80x9cFlammerxe2x80x9d) which is herein incorporated by reference. Flammer describes a wireless packet communication system having a plurality of nodes, each having a transmitter and a receiver, the receiver at each node is assigned a seed value and is provided with a channel punchout mask, i.e., channel mask. A node uses its seed value and channel mask to generate a specific randomly ordered channel hopping band plan on which to receive signals. A node transmits its seed value and channel mask to target nodes with which it wants to establish communication links, and those target nodes each use the seed value and channel mask to generate the randomly ordered channel hopping band plan for that node.
A problem in a microcellar system is foreign interference, namely interference which is from transmitters outside of the control of network devices of the microcell system. Some of these interferers may share some of the frequency hopping channels of one or more network devices and cause errors in data received by the network devices. Thus there is a need to identify interference on channels of a network device and to adjust the channel mask of the device to reduce the interference.
The present invention provides a method and a system for determining a channel mask in a network device in a microcellar network. An exemplary embodiment uses a weighted average of the background noise on a channel of the network device to determine whether a particular channel should be masked out.
One embodiment of the present invention provides a method for selecting a group of channels from a plurality of frequency hopping channels received by a wireless communications device, the channels in the group being excluded from receipt by the wireless communications device. The method includes the steps of determining an indicator based on a received noise measurement at a first time for a channel, then determining a weighted average at a second time for the channel, the weighted average including the indicator, and then selecting the channel as a member of the group, upon an indication that the weighted average at the second time is above a threshold. The threshold may include a fixed number above a noise floor. The noise floor is a minimum of the weighted averages, where a weighted average is determined for each channel. The threshold may be increased by a unit until the frequency hopping channels, excluding the group of channels, are greater than or equal to a number N.
In another embodiment, a network device for determining a channel mask in a microcellar communications network is provided. The network device includes a digital signal processor (DSP) and a memory. The DSP has a component, which could be software, to measure background noise for a frequency at various times. The memory has software including a data structure having a weighted average of background noise for the frequency and selection software for setting the frequency as a hopping frequency of the channel mask, when the weighted average is below a threshold.